devil: Remove old device status file in device_monitor.
devil: Remove old device status file in device_monitor.

R=jbudorick@chromium.org
BUG=chromium:670879

Review-Url: https://codereview.chromium.org/2781423002

benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult,benschmaus/catapult,benschmaus/catapult,catapult-project/catapult,catapult-project/catapult-csm,catapult-project/catapult-csm,catapult-project/catapult,catapult-project/catapult-csm,benschmaus/catapult,catapult-project/catapult-csm,benschmaus/catapult,benschmaus/catapult